There is a high incidence of inner ear diseases such as progressive sensorineural hearing loss, sudden deafness, otosclerosis and Meniere's disease. The etiology of these inner ear diseases remains unclear or unknown. However, evidence now suggests that certain inner ear diseases, including those above, appear to be of autoimmune origin. In patients with inner ear disease, several attempts have been made to identify specific antigens with which circulating antibodies and active lymphocytes react. Antibodies against type II collagen and heat shock protein p70 have been described in patients suffering from idiopathic inner ear disease (e.g. Yoo et al., Science 1982, 217, 1153–1155).
It is known that the 30,000-Mr (30 kDa) protein present in guinea pig inner ear is recognized by autoantibodies in sera from patients with inner ear disease. The 30,000-Mr inner ear antigen has been partially purified by chromatography (M Y Cao et al., Mol Cell Biochem. 1995, 146, 157–163). This inner ear antigen has now been sequenced, and partial internal sequences and N-terminal sequence (in total 84 amino acids) of this protein have been obtained. It has been found that the 30 000-Mr inner ear protein is the major myelin protein zero (MPP, Pzero, Po). The complete sequence of the bovine, rat, mouse, chick, and human proteins has been determined. Each contains 229 amino acids and a signal peptide of 29 amino acids. Po is highly conserved between species and the interspecific replacement rate of Po between human and guinea pig is very low.